1. Field of the Invention
The present disclosure relates to a method of preparing copper nanostructures with various morphologies, and specifically, to a method of preparing copper nanostructures with various morphologies by reducing a copper precursor compound in an aqueous solution, in which halide ions are used to prepare the copper nanostructures in a more efficient and easier manner.
2. Description of the Related Art
Metal nanoparticles are diversely utilized in electronics, optics, catalysts, and biological fields due to their physicochemical properties. Specifically, metal nanoparticles having electrical conductivity may be used to prepare conducting films, and therefore, metallic nanoparticles have received considerable attention in the fields of smart windows, rewritable electronic papers, electronic panel displays, flexible displays, etc. Particularly, copper is a metal that attracts much attention due to excellent electrical conductivity and low cost.
These metal nanoparticles may be prepared by various methods including a reduction-precipitation method in an aqueous solution, an electrochemical method, an aerosol method, a reverse microemulsion method, a chemical liquid phase deposition method, a photochemical reduction method, and a chemical reduction method in a solution, etc. However, such preparation methods are either very complicated or exhibit very low yield, and thus there has been a need for the development of a novel improved method.
On the other hand, since particle characteristics (unique plasmonic effect) vary depending on the shape and size of nanoparticles, many efforts have been made to control their shape and size.
For example, two-dimensional (2D) nanostructure such as nanodisks, nanosheets, and nanoplates has great physical and chemical properties because of their high aspect ratio of the size and thickness. A plate-shaped, copper nanostructure having 2D nanostructure is also a promising alternative novel metal material in flexible conductors because of its excellent electrical conductivity, flexibility, and transparency. However, the previous methods of preparing the plate-shaped copper nanostructures are not appropriate for large-scale production of high-quality plate-shaped copper nanostructures with sharp edges over a wide size range of 10 μm. As one of the previous methods of preparing the plate-shaped copper nanostructures, there is a method of reducing Cu(OAC)2 with hydrazine in the presence of poly(vinyl pyrrolidone) (PVP) under the oil-phase.
To date, the aqueous synthesis methods have been considered. One of them is a method of reducing CuCl by using ascorbic acid in the presence of cetyltrimethylammonium bromide (CTAB) as a capping agent. However, this method requires a high reaction temperature of 120° C., and the resulting plate-shaped copper nanostructures are as short as 1-3 μm in edge length.
Another method is to use polyvinylpyrrolidone (PVP) as a capping agent and potassium sodium tartrate as a complexing agent in synthesis of the plate-shaped copper nanostructures. However, there are problems that this method takes a long time (24 hrs) at a relatively high temperature (100° C.), and the resulting plate-shaped copper nanostructures are shorter in edge length (0.18 μm˜0.28 μm).
Furthermore, there is a method of synthesizing wire-shaped copper nanostructures using ethylenediamine (EDA) as a capping agent and polyvinylpyrrolidone (PVP) as a stabilizer. However, this method requires multiple steps and the resulting wire-shaped copper nanostructures are as short as 10 μm˜20 μm. Therefore, there is a demand for a simple and economic method capable of synthesizing high-quality long copper nanostructures.
Accordingly, the present inventors have completed a method capable of preparing copper nanostructures with various shapes in a simple manner, in which the copper nanostructures show long-term stability without formation of copper oxides on the surface of copper nanostructures.